1. Field of the Invention
The present invention relates to a composition containing an aqueous dispersion of lipid vesicles based on carbamate with a cholesteryl chain and to its use in topical application.
2. Discussion of the Background
Dispersions of lipid vesicles are well known in the cosmetics field or in dermopharmaceuticals. Some amphiphilic lipids possess the property of forming mesomorphic phases, the state of organization of which is intermediate between the crystalline state and the liquid state, and some of them are capable of swelling in the presence of an aqueous solution to form a lamellar phase and, after agitation, to form vesicles or spherules dispersed in an aqueous phase. These vesicles are formed by a membrane composed of substantially concentric sheets containing one or more multimolecular layers, preferably bimolecular layers, encapsulating an aqueous phase.
Among lipids capable of forming lipid vesicles, amide compounds comprising a group derived from sugars, such as D-mannose, D-galactose and D-glucose, are known according to application WO-A-83/04412.
The above-mentioned vesicles can be prepared by numerous known processes.
According to a first process, which is described, for example, by Bangham et al. (J. Mol. Bio., 13, 1965, pages 238 to 262), the lipid phase is dissolved in a volatile solvent, and a thin film of lipid phase is formed on the walls of a flask by evaporation of the solvent. The aqueous phase to be encapsulated is then introduced to the lipid film and the mixture is agitated mechanically until a dispersion of vesicles having the desired size is obtained; an aqueous dispersion of vesicles encapsulating an aqueous phase is thus obtained. This process requires the use of a solvent during the preparation of the lipid phase.
According to a second so-called "by comelting of the lipids" process, which is described in, for example, FR-A-2,315,991, the lipid phase is prepared by mixing amphiphilic lipid(s) and optional additives at a temperature at which the mixture is molten. If the mixture is not liquid at room temperature a lamellar phase is formed by introducing the aqueous phase to be encapsulated then dispersing the lamellar phase in the form of vesicles using an ultradisperser, a homogenizer or ultrasound, in an aqueous dispersion phase. This process requires heating the lipids in order to reach their melting temperature.
To obtain dispersions of lipid vesicles which are stable over time, it is known, for example, from application EP-A-582,503, to combine, with the lipids, an additive capable of improving the encapsulation properties of the lipid membrane. Cholesterol is the additive most commonly used for this purpose. However, the preparation of these stable vesicle dispersions requires an additional stage for incorporating the additive in the lipid mixture.
Thus, the above-mentioned conventional processes require numerous stages to prepare the dispersions of lipid vesicles and these stages make the processes rather complex to employ. In addition, aqueous dispersions of vesicles are not always stable over time, depending on the lipids present in the lipid phase of the vesicles. The instability can be due, for example, to the recrystallization of certain lipids in the membrane of the vesicles or to the oxidation over time of the lipids or alternatively due to the disintegration of the structure of the lipid membrane.
It is desirable for the lipid vesicles to possess good encapsulation properties in order to make it possible to transport active ingredients according to the desired application. Thus, in addition to solving the above-mentioned problems, it is desirable to obtain lipid vesicles having good permeability.